200 
Collie—Geology of Conanicut Island, B. I. 
rocks of this area are coarse granite rocks and compact flinty 
slates. The hard resistant rocks give rise to the rough, 
knobby topography found in the southern part of Conanicut, 
which exhibits so striking a contrast to the smooth surface fea¬ 
tures of the other parts of the island. 
STRATIGRAPHY. 
The indurated formations of the island resemble in character 
and in order of superposition those found about Newport and 
the small islands scattered through Narragansett Bay. In 
many respects the stratigraphy is closely allied to that found 
farther north in this same basin. There are four formations 
which are as follows in order of age: 1st. A compact non- 
fossiliferous slate. 2d. A coarse grained porphyritic granite. 
3d. An extensive series of schists, interbedded with beds of 
grit and fine conglomerate. In the lower portion of this series 
carboniferous plants have been found, but as a whole these beds 
are non-fossiliferous. 4th. A series of dikes which cut both 
granite and schists. In all of these formations innumerable 
veins of quartz, calcite, pegmatite and chlorite are found, occu¬ 
pying every joint, fissure aad crevice. 
Metamorphism aside, the geology of the island is extremely 
simple. The more unaltered slates and schists indicate this. 
The original lithological constitutents were few, the conditions 
attending deposition were simple. Metamorphism, however, has 
altered all of this primal simplicity. This agency working hand 
in hand with secondary change has greatly increased the num¬ 
ber of minerals, and since each of these minerals combines into 
masses by itself very frequently, the result is a great increase 
in the number and variety of the formations. The original sedi¬ 
mentary rocks contained grains of quartz and feldspar, and more 
rarely flakes of iron oxide, graphite, and ferro-magnesian silicates. 
These ingredients made up the rocks. Metamorphism has intro¬ 
duced as additional minerals sericite, ottrelite, staurolite, 
chlorite, tourmaline and andalusite. The sericite and ottrelite 
are sufficiently abundant to form distinct strata and formations; 
the great mass of the schists are sericites chists; imbedded in these 
are found ottrelite schists; and these two distinct formations have 
